With a rapid increase in the use of fossil fuels, there is an increasing demand for use of alternative energy or clean energy. The field of electricity generation and accumulation using an electrochemical reaction has been most actively studied to meet the increasing demand.
As a representative example of electrochemical devices using such electrochemical energy, secondary batteries are currently used and an application area thereof has gradually been increased. Recently, with an increase in development of technology and demand for portable devices, such as portable computers, mobile phones, cameras, and the like, demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, much research on lithium secondary batteries, which have high energy density, high operating voltage, a long cycle lifespan, and a low self-discharge rate, has been conducted, and such lithium secondary batteries are commercially available and widely used.
Generally, a secondary battery consists of a positive electrode, a negative electrode, and an electrolyte. In the secondary battery, lithium ions released from a positive electrode active material are intercalated into a negative electrode active material such as carbon particles through 1st charging and the lithium ions are deintercalated through discharging. As lithium ions reciprocate between opposite electrodes as such, they transfer energy. Therefore, the secondary battery can be charged and discharged.
For example, the lithium secondary battery has a structure in which a lithium electrolyte is impregnated into an electrode assembly consisting of a positive electrode including a lithium transition metal oxide as an electrode active material, a negative electrode including a carbon-based active material, and a porous separator. The positive electrode is manufactured by coating an aluminum foil with a positive electrode mixture including a lithium transition metal oxide, and the negative electrode is manufactured by coating a copper foil with a negative electrode mixture including a carbon-based active material.
Meanwhile, lithium is precipitated in a negative electrode including a negative electrode active material such as natural graphite during charging, and thus battery performance may be degraded. Also, when silicon is used as a negative electrode active material, capacity is high, but battery performance may be degraded due to repetition of expansion and contraction caused by charging and discharging.
Therefore, a negative electrode for a secondary battery, which has high capacity and longer lifespan characteristics, is required.